1. Field of the Invention
This invention relates to a method for measuring a concentration of CaCO.sub.3 and/or CaSO.sub.3 in slurries comprising CaCO.sub.3 and/or CaSO.sub.3 therein.
2. Description of the Prior Art
Typical of slurries comprising CaCO.sub.3 and/or CaSO.sub.3 is, for example, an absorption solution used in flue gas desulfurization systems using a wet lime gypsum process. The performance of the flue gas desulfurization system is so controlled that an absorbent such as CaCO.sub.3 or Ca(OH).sub.2 is added in amounts sufficient for stoichiometric absorption of SO.sub.2 in order to keep the pH of the circulating absorption solution in an absorption tower at a predetermined level.
In recent years, there is the high tendency toward savings of resources or energy and even apparatus which generate exhaust gases such as boilers are now designed to attain high efficiency. In operation, the load variation speed becomes high and thus it will be necessary to follow such a load variation without impeding the performance in the flue gas desulfurization system.
It has been confirmed that in the flue gas desulfurization systems, when the wet lime gypsum process is used, it is difficult to maintain high performance in relation to such a high speed load variation over an entire period by the use of the currently employed pH control system of circulation an absorption solution in an absorption tower. This is because even if the pH of the absorption solution is controlled at a level, the concentration of CaCO.sub.3 and/or CaSO.sub.3 in the absorption solution varies depending on the variation in the desulfurization load.
The present inventors have extensive studies of a method which can overcome the above difficulties and which can follow the high speed load variation of the exhaust-generating apparatus and maintain good desulfurization performance over an entire period. As a result, it has been found that if a concentration of CaCO.sub.3 and/or CaSO.sub.3 in absorption solution is known prior to use thereof, it is possible to provide a measure of maintaining the desulfurization performance against the load variation, thus leading to a method of measuring a concentration of CaCO.sub.3 and/or CaSO.sub.3 according to the invention.
According to the present invention, there is provided a method for continuously measuring the concentration of CaCO.sub.3 and/or CaSO.sub.3 in slurries comprising CaCO.sub.3 and/or CaSO.sub.3, the method comprising:
continuously sampling a given amount of the slurry;
feeding the slurry to an agitated continuous reactor container which is isolated from the outside air;
keeping the slurry in the reactor container at a temperature not lower than 70.degree. C. and to which is added sulfuric acid or hydrochloric acid to adjust the pH to below 3;
blowing air or nitrogen gas into the slurry in the reactor container;
withdrawing from the container CO.sub.2 and/or SO.sub.2 produced by reaction between CaCO.sub.3 and/or CaSO.sub.3 and the acid by entrainment with the air or nitrogen gas; and
calculating the concentration of CaCO.sub.3 and/or CaSO.sub.3 in the slurry from the concentration of CO.sub.2 and/or SO.sub.2 in the withdrawn gas, the flow rate of the sampled slurry and the flow rate of the blown air or nitrogen gas.
Moreover, the concentration of CaCO.sub.3 and/or CaSO.sub.3 in the slurry may be determined by further mixing the withdrawn gas with air or nitrogen gas and calculating the concentration from the concentration of CO.sub.2 and/or SO.sub.2 in the mixed gas, the flow rate of the sampled slurry, the flow rate of the blow air or nitrogen gas, and the flow rate of the air or nitrogen gas being mixed.